Abstract:
High peak-to-average-power ratio of OFDM-based 3G/4G and 5G communication signals forces the power
amplifier (PA) at the transmitter to work at reduced efficiency. In order to operate the PA with maximum
possible efficiency, the OFDM-based signals are processed before transmission such that their PAPR is
reduced. Clipping and filtering is one of the simplest and most effective methods to reduce the peak power
of multi-carrier signals. Although it reduces PAPR efficiently, the in-band distortion and out-of-band
distortion produced post-clipping operation degrades the system performance. The former leads to signal
quality degradation deteriorating the bit error rate (BER) performance of the system and the latter is
responsible for spectral fading.
The present work analyzes the variants of conventional clipping and filtering technique so as to achieve
optimum PAPR reduction. A signal smoothening technique is also proposed that is intended to suppress the
frequency distortion due to signal clipping. Based on this approach, two algorithms viz. two-point
polyBLAMP and four-point polyBLAMP are presented and tested for sinusoidal, harmonic and LTE
signals. The results show that the aforementioned technique works well with sinusoidal and harmonic
signals producing aliasing suppression of more than 10 dB. In order to mitigate the clipping noise distortion
and restore the BER performance of the system, several receiver-based processing techniques are presented.
Based on this, an RRC-OFDM system is proposed which involves optimized iterative clipping and filtering
at the transmitter and receiver-based iterative recovery of clipping noise. It includes the use of root-raisedcosine
(RRC) filtering in order to improve the spectral efficiency in OFDM-based communication. The
simulation results show significant increase in power efficiency of PA ( 21%) after the application of
transmitter-based optimized clipping algorithm with relatively lesser increase in SNR ( 2 dB) to achieve
the same BER performance as that of the non-clipped case.
